Water well water level sensor (indicator)

Question

I have a 400ft well, and I want to have a buzzer comes on every time water drops below certain level(280ft). At the moment, I got it working using a 12V battery and a multi-meter. I dropped down an electrical wire(2 wires). Now the top ends are connected as follow: One to Battery Negative and the other to Multi-meter negative. Multi-meter positive is connected to Battery Positive. This works fine, and the multi-meter reads 12V whenever the wire is submerged in the water. No reading when it's not.

Like I said at the beginning, I would like to have a buzzer, so I tried it using a transistor, a buzzer and couple resistors. Since water is not a good conductor, it did not work. The only way it worked is by adding a cork. The cork is hollow, and I inserted a metal plate, so water lifts or drops the cork for contact. I also tried a five pin normally open/ normally closed relay. Same result, not enough amperage to trigger the relay. Had to use the cork again. The cork won't fit thru the well. Testing was done outside the well.

Now the Pros of this method: I feel like I could do it.

Cons: Am I creating some electrolysis that eventually corrode the copper wires?

Anything other suggestions or different ways? What about using arduino ? Could it act as a voltage sensor like a multi-meter then triggers a relay or something? Any ideas will be appreciated.

Thank you

Answer 1

Why not make a tilt switch that you drop down.

As the water rises the switch floats and as it is pivoted on one side it tilts and a ball in a tube rolls down to make the contact (or break the contact as preferred).

That way all the contacts are sealed in a tube so no corrosion due to water will happen.

Answer 2

Cons: Am I creating some electrolysis that eventually corrode the copper wires?

Yep, things like moisture sensors for soil use the same method as your wires dangling into the water. They're typically platinum-coated.

Copper has very reliable surface corrosion, very quickly; really not the material of choice for perfect conduction. It's the material of choice for water pipes for the same reason: the surface gets a good coating of copper oxide, which protects the rest of the pipe very well. That's awesome!

This bad news is good news in disguise:

1. yes, this works (in principle)
2. yes, there's enough commercial products that do it like that, and you can buy such electrodes
3. since you really don't need much current to flow (you might need a better amplifier circuit than the unspecified transistor you had), this is really relatively easy
4. if you can live with the added resistance of a corroded copper surface, this will work with simple wires for years. Make sure the current that flows is really small (series resistor!) and amplified sufficiently (multiple stages of transistors, or much simpler, an opamp amplifier circuit, and a single transistor just to switch the relay), and filtered for radio interference (long wires are antennas...) with a trivial capacitor to ground after the series resistor, and you will have years of joy with your copper electrodes.